The present invention relates to an imaging method using a nuclear magnetic resonance (hereinafter referred to as NMR) phenomenon, and more particularly to such a method suitable for acquisition of a crude image during or exactly after measurement in a three-dimensional imaging.
In an imaging using an NMR phenomenon, it is necessary to separately identify the signal from an object. According to one of methods which are generally used, a read-out field gradient is applied or a gradient along one direction is provided to the intensity of a static magnetic field during a signal detection period of time to provide a gradient to a resonance frequency. Further, there is well known a method which is used in combination with the above-mentioned method and in which a phase encoding field gradient is applied or a gradient along a second direction is provided in a period of time from the excitation of spins until the detection of a signal to encode the phase of spins with information of the location along the second direction. The basic concept of this method is described by, for example, Journal of Magnetic Resonance, Vol. 18, pp. 69-83 and PCT Patent Application No. GB81/00044 (WO81/02788). The Journal of Magnetic Resonance also describes a three-dimensional imaging in which a phase encoding field gradient along a third direction is further applied.
In an imaging using the above-mentioned phase encode, it is required to repeat the measurement of a signal while changing the encode value (in general, the magnitude of the phase encoding field gradient) by the number of times corresponding to the number of locations to be separately identified. In the three-dimensional imaging in which phase encoding is made for two directions, measurement is repeated with all combinations of a plurality of magnitudes of gradient prepared for a phase encoding field gradient along one of the two directions and a plurality of magnitudes of gradient prepared for a phase encoding field gradient along the other direction.